Amplifier circuits are used in a variety of devices and applications. Advances in technology have led to a demand for increased functionality, decreased costs and higher efficiency. There have been a number of efforts to develop amplifier circuits to meet these and other demands. In the field of communications systems, for example, there have been extensive efforts to increase the data throughput of the systems. These efforts have often resulted in increased power consumption/dissipation due to factors such as increased chip density, higher signal speeds and precise signaling protocols. Moreover, the communications and other fields have also exhibited significant growth in portable devices. Demand for smaller and more powerful portable devices is often limited by power constraints, such as battery life and power dissipation. Accordingly, a need exists for an amplifier circuit that exhibits high power efficiency, low complexity and high accuracy.
Signal processing circuits used in communications and other systems often require the use of several amplifier circuits. For instance, many signal processing circuits are implemented using one or more analog-to-digital converters (ADC). Amplifier circuits are a major component of many ADCs, both in terms of the functionality and power consumption. For instance, the amplifier circuit often dominates the power consumption of a pipelined ADC because the ADC has an amplifier circuit for each stage of the pipeline. Generally, as the frequency and accuracy of an ADC increases, the power consumption of the amplifier circuits increases. Significant efforts have been made to reduce the power consumption of ADCs, including the amplifier circuits, but there is significant room for improvement.
Amplifier circuits are often constructed using one or more semiconductor devices arranged to amplify an input signal. Often these gates are field-effect-transistors (FET), such as metal-oxide-semiconductor (MOS) field-effect transistors. Typical amplifier circuits receive an input signal and produce an amplification of the input signal by driving an output load. For many FET amplifier circuits, a significant portion of power dissipated by the circuit is not used to drive the load. For instance, a differential-pair amplifier circuit steers a current between two paths, each having a FET. As the output nears the desired voltage, the circuit primarily dissipates the current primarily through the transistors rather than applying the current to the load. This results in a less than trivial amount of power being wasted. Moreover, even where the load is small or nonexistent, significant power dissipation exists.
These and other issues have presented challenges to the implementation and design of amplifier circuits, including those involving switched-capacitor circuits and similar applications. Accordingly, there is a need for an amplifier circuit that provides sufficient accuracy and efficient power consumption.